1. Field of the Invention
The present invention relates to a method of producing an organic based fertilizer and, in particular, to a method of producing an organic based fertilizer from animal waste in a closed loop system that conserves water.
2. Description of the Related Art
In modern agricultural practice, it has become usual to employ an agricultural operation as an intensive feeding operation for raising hundreds or even thousands of livestock, for example swine and bovine animals, at a single location. Consequently, large amounts of animal waste are produced at such locations. The disposal of this waste in a hygienic and inoffensive manner is problematic.
More particularly, it has been suggested that hogs produce more than four times as much waste as humans. It has, for example, been planned to initiate a hog farm containing 2,000,000 hogs, which will produce an amount of waste equivalent to that produced by the city of Los Angeles. The current pig population of North Carolina is four times that number. Accidents in North Carolina, in which millions of gallons of hog excreta were released into the countryside, have drawn attention to the problems involved in the disposal of such waste. Applications for permits to construct large hog farms have been denied because of concerns about odours and waste disposal.
Animal waste, including hog waste, has traditionally been disposed of by spreading it over agricultural land as a liquid fertilizer. For sufficiently large cropped land bases this method of disposal can be performed safely. However, in areas of high population density or where multiple farms are closely clustered, and the land base is therefore relatively small, problems arise. For example, excess nutrients cannot be absorbed by crops and leach into ground water and surface water.
When land application is prevented, for example, because the ground is frozen or saturated with water and/or nutrients, the waste must be stored, usually in large pits, with consequential costs and environmental risk.
As an alternative to land disposal, it is also common practice to compost the waste. For this purpose, the waste is separated into solid waste and liquid waste through the use of inclined screens, sometimes followed by the use of belt or filter presses. These methods produce an output containing about 30% solid material at best. This is then mixed with a bulking material to facilitate aeration and an appropriate C:N ratio, and deposited in windrows for stabilization, over a period of about 45 to 60 days, by composting. This process may not ensure that pathogens in the waste are killed and the windrows are often odorous and may attract birds, rodents and vermin. The liquid, approximately 90% of the total waste still has to be dealt with through land application.
The challenges involved in the treatment of animal waste include the destruction of pathogens, the controlled extraction of ammonium and other plant nutrients, and the disposal of organic matter.
It is known, from U.S. Pat. No. 4,093,544, issued Jun. 6, 1978, to David S. Ross, the full disclosure of which is incorporated herein by reference, to remove ammonium from wastewater by firstly increasing the pH value of the wastewater, then desorbing ammonium by vacuum and subsequently absorbing the desorbed ammonium in liquid having a pH value and temperature substantially less than that of the original wastewater.
It is further known from U.S. Pat. No. 5,914,040, issued Jun. 22, 1999, to Yvette Pescher et al., the full disclosure of which is also incorporated herein by reference, to purify a medium containing organic waste, for example animal waste, by subjecting the medium to treatment with an oxidizing agent, treatment with a flocculating agent, and treatment with at least one polyelectrolyte. The effluent thus obtained is filtered to provide a filtration cake and a filtrate.
It is still further known from U.S. Pat. No. 6,916,426, issued Jul. 12, 2005, to Van Slyke et al., the full disclosure of which is also incorporated herein by reference, that the extraction of nitrogen, potassium, and phosphorus from animal waste is substantially enhanced if the animal waste is treated promptly after production of the waste by the animals. More particularly, it is known that potassium is present in animal waste material in the form of an insoluble potassium urate, and a substantial amount of the potassium in animal waste material can be extracted in a solid form, as potassium urate, before microbial action breaks down the potassium urate to leave potassium and ammonium in solution. Extracted urates are then available for inclusion in a fertilizer. When the fertilizer is used on land, the microbes in the soil break down these urates, releasing the potassium and ammonia, but at a rate less than that at which these nutrients would be released in the soil if dissolved in water.
It is yet still further known from U.S. Pat. No. 7,232,036, issued Jun. 19, 2007, to Van Slyke et al., the full disclosure of which is also incorporated herein by reference, that solid waste may be rapidly separated from liquid waste using an inclined conveyor belt system.